The invention relates to thermal management in a system.
Different types of power and thermal management techniques have been implemented in systems. A simple system includes a sensor that detects for an over-temperature condition and generates an interrupt to cause the computer system to shut down or otherwise go into a low power state (typically by deactivating components) when the over-temperature condition is detected. Another more sophisticated technique is defined by the Advanced Configuration and Power Interface (ACPI) Specification, Rev. 1.0, published on Dec. 22, 1996, that provides an interface between the operating system of a system and hardware devices to implement power and thermal management.
The ACPI specification defines several thresholds that indicate temperatures at which different levels of software-controlled thermal management activities are performed. Three primary cooling policies are defined in the ACPI specification: passive cooling (in which the operating system reduces the power consumption of the system by throttling the processor clock); active cooling (in which the system expends energy to reduce power by taking a direct action such as turning on a fan or remote heat exchanger); and critical trip control (in which a threshold temperature has been reached at which the operating system performs a critical shutdown of the system).
Passive cooling as defined in the ACPI specification involves a type of thermal management known as throttling of one or more central processing units (CPUs). Under ACPI, the operating system (OS) can program varying CPU clock duty cycles so that the power dissipation of the CPU matches the power dissipation capabilities of the system. To accomplish throttling, clocks in the CPUs are enabled and disabled according to the defined duty cycle.
According to the ACPI specification, two execution states are defined for the CPU, one a full speed state and one a throttled state (in which the CPU clocks are active only a programmed percentage of the time). While in the throttled state, the CPU""s clock is stopped a programmed percentage of the time, which may reduce overall system performance if the CPU remains in the throttled state for an extended period of time for system temperature control.
A need thus arises for a thermal management technique that is capable of maintaining system performance at a relatively high level.
In general, according to an embodiment, a system includes a component having a clock and a thermal management controller adapted to vary the component between performance states including a lower performance state when the controller detects a first condition, the controller adapted to throttle the clock while the component is in the lower performance state.
Other features will become apparent from the following description and from the claims.